iOS: popViewController unexpected behavior

Question

I've been searching the internet for a solution. There's nothing I could find. So: I'm using a UINavigationController. I am pushing two UIViewControllers onto it. In the second pushed ViewController i am executing this code:

- (void)reverseGeocoder:(MKReverseGeocoder *)geocoder didFailWithError:(NSError *)error {
NSLog([error localizedDescription]);
[self.navigationController popViewControllerAnimated:YES]; }

The expected thing to happen would be that the last pushed ViewController disappears. In this app I am doing this on few places and it works fine everywhere expect in this very ViewController. What happens is that only the back button goes off screen (animated) but everything else stays on screen. In the Console Output two things are printed out when this line executes:

2011-03-14 16:32:44.580 TheAppXY[18518:207] nested pop animation can result in corrupted navigation bar

2011-03-14 16:32:53.507 TheAppXY[18518:207] Finishing up a navigation transition in an unexpected state. Navigation Bar subview tree might get corrupted.

Two error messages I couldn't find ANY information on. I'm using XCode 4 and iOS SDK 4.3. Maybe anyone can help me with this problem.

Answer 1

I came across a similar situation in my code and the message said:

nested push animation can result in corrupted navigation bar

Finishing up a navigation transition in an unexpected state. Navigation Bar subview tree >might get corrupted.

My finding to this issue was that I was pushing 2 view controllers one after the other in quick succession and both were animated.

In your case it seems that you might be popping multiple view controllers with animation one after the other.

Hence, while one view is undergoing animation you should not start animation on another view.

I also found that if I disabled animation on one view, the error message disappeared.

In my case it was a problem with the flow logic as I did not intend to push 2 view controllers one after the other. One was being pushed within the switch case logic and another after its end.

Hope this helps someone.

Answer 2

You can get this anytime that you try to pop before viewDidAppear. If you set a flag, then just check that flag in viewDidAppear, you wont have a problem.

Answer 3

I have created a drop-in replacement for UINavigationController that will queue animations for you and avoid this problem entirely.

Grab it from BufferedNavigationController

Answer 4

I had this problem, too, and here's what was causing mine:

1. In RootViewController, I am using several UISegmentedControl objects to determine which of many views to load next.
2. In that (sub/2nd) view, I was popping (by using the "Back" button) back to RootViewController.
3. In RootViewController, I was handling viewWillAppear to "reset" each of my UISegmentedControl objects to a selectedSegmentIndex of -1 (meaning no segment looks "pressed").
4. That "reset" triggered each of my UISegmentedControl objects to fire their associated (and separate) IBActions.
5. Since I wasn't handling for a "selection" of -1, I had multiple methods firing at the same time, all trying to push a different view.

My fix? I tightened up my if...then statements and bailed on executing any code in my UISegmentedControl IBActions when selectedSegmentIndex == -1.

I'm still not sure why I got "pop" animation errors and not "push" errors, but at least figured out my error and got it fixed!

Hope this helps someone else!